Previously, MongoDB operations that required the JavaScript interpreter
had to acquire a lock, and a single mongod could only run a
single JavaScript operation at a time. The switch to V8 improves
concurrency by permitting multiple JavaScript operations to run at the
same time.

V8 does not support the non-standard destructuring assignments.
Destructuring assignment “extract[s] data from arrays or objects using
a syntax that mirrors the construction of array and object literals.” -
Mozilla docs

Example

The following destructuring assignment is invalid with V8 and
throws a SyntaxError: